One problem that is prevalent in mills for making paper pulp is effective utilization of space. Also, mill construction costs are high, especially when--as in many modern mills--the vessels used for production of pulp are large, sometimes having a height of well over a hundred feet.
According to the present invention, a method and apparatus are provided which address these two problems in modern paper mills. According to the present invention, support for a number of accessory vessels is provided by already existing main vessels, such as the continuous digester itself and an impregnation vessel, if present. The continuous digester is typically the largest vessel found in the pulp mill, often extending to heights of over a hundred feet, and having excellent structural integrity. Because the digester vessel must be capable of holding large volumes of wood chips, or other comminuted cellulosic fibrous material, and liquid slurry under high pressure and temperature conditions, it is a massive, well-built, structurally sound vessel.
According to the invention, the structural integrity of the continuous digester is taken advantage of in providing an arrangement of components that minimizes the amount of structural steel that is necessary in order to support all of the components normally associated with the pulp mill while effectively utilizing space. As a matter of fact, according to the invention, it is possible to provide ready maintenance areas for a number of the vessels while also achieving the objectives set forth above.
According to one aspect of the present invention, a method of structurally supporting accessory vessels cooperating with an upright continuous digester for producing paper pulp from comminuted cellulosic fibrous material, is provided. The method comprises the steps of (a) providing a first structural support extending outwardly from a side of the digester, between the top and bottom thereof with expansion joints, such as on bridges, to compensate for the thermal expansion from the cold (non-operating) to the hot condition (operating); (b) providing a second, vertical, structural support independent of the digester and adjacent to it; and (c) operatively connecting at least one accessory vessel which feeds liquid or material to, or receives liquid or material from, the digester, to the first structural support so that the accessory vessel is vertically supported by the digester and the second vertical supports.
The at least one accessory vessel preferably comprises a chip bin with a horizontal steaming vessel mounted under the chip bin on a separate support system. It is also preferable to provide the further steps of providing a third structural support extending outwardly from the opposite side of the digester, providing a fourth vertical, structural support independent of the digester and adjacent to it; and operatively connecting an additional accessory vessel to the third structural support so that that additional accessory vessel is vertically supported by the digester and the second vertical supports, and no other structures.
A second vertical structural support provided according to the invention may be an impregnation vessel, while the fourth structural support comprises a pair of vertical beams or legs. The first and third structural supports comprise generally horizontally extending pairs of beams from the digester's opposite sides, the beams engaging side supports or portions of the accessory vessels, and cross members preferably being provided between the beams at the accessory vessels.
The invention also comprises a superstructure assembly of vessels. The superstructure comprises an upright continuous digester having a top, bottom, and sides, a material inlet to the top, and a pulp inlet from the bottom, and containing a slurry of material and liquid; an accessory vessel connected to the digester to feed liquid or material to the digester, or receive liquid or material from the digester; a first structural support extending outwardly from a side of the digester, and vertically supported by the digester; a second, vertical, structural support adjacent to, but spaced from, the digester, and connected to the first structural support to assist the digester in vertically supporting it; and the accessory vessel engaging and vertically supported by the first structural support.
The invention--according to another aspect--also comprises the following: An upright continuous digester having first and second, opposite sides. An upright impregnation vessel adjacent, but spaced from, the digester. A chip bin. A flash tank. A first pair of generally horizontally extending beams connected at one end to a first side of the digester and at the opposite end to the impregnation vessel, the chip bin being supported only by the first pair of beams and elements connected thereto. This connection would be designed to accommodate for thermal expansion. A pair of vertical legs adjacent, but spaced from, the digester and spaced apart a distance roughly corresponding to the diameter of the digester. A second pair of generally horizontal beams connected to the second side of the digester and extending therefrom to the vertical legs. And, the flash tank being supported only by the second horizontal beams and structures connected thereto.
It is the primary object of the present invention to provide for the effective utilization of space in a pulp mill and to minimize the amount of structural steel necessary for supporting the vessels utilized for the production of paper pulp in the mill. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.